A compressed air processing apparatus is known from German Patent No. DE 195 44 621 C1 corresponding to European Patent No. EP 0 776 807 B1. The apparatus includes a common structural unit in which the pressure controller, the air dryer and a multi-circuit protection valve are combined. The multi-circuit protection valve includes a plurality of overflow valves having limited backflow, each of the overflow valves being associated with one of the circuits of the apparatus. Conduits lead from the overflow valves to containers of which each one is associated with one of the circuits. Usually, the containers of circuits I and II are associated with the two circuits of the operational brake system of the motor vehicle. Additional circuits serve to supply the parking brake valve as well as secondary aggregates. In this way, there may be a fifth circuit including an overflow valve of the multi-circuit protection valve and leading to a reservoir container via a conduit. Air suspension of the motor vehicle is connected to the reservoir container. In this way, the air suspension system of the motor vehicle is supplied with compressed air, and it is protected.
Another compressed air processing apparatus is known from German Patent No. DE 196 38 226 C1 corresponding to European Patent No. EP 0 831 383 B1. The known apparatus includes a fifth circuit including a reservoir container being protected by an overflow valve.
A method for filling an air suspension system by an air dryer is known from German Patent Application No. DE 100 38 266 A1. A compressor and an air dryer located downstream of the compressor exclusively serve to supply and control the air suspension system. A check valve is bypassed by a throttle. Downstream of the check valve, supply conduits lead to controllable directional valves being located upstream of the respective air suspension bellow. Furthermore, there is an escape valve which is a component of a pressure controller. The pressure controller may also be operated for regeneration of the air dryer. An electronic control unit is associated with the air suspension system. The electronic control unit exclusively controls the elements of the air suspension system and of the associated compressed air processing apparatus.
It is generally known in the field of motor vehicles, especially trucks, to supply the motor vehicle with a pneumatic brake system and a pneumatic air suspension system. The air suspension system is supplied with compressed air by one circuit of the compressed air processing apparatus. This circuit is arranged in addition to the brake circuits. Usually, the air suspension system connected in this way includes a plurality of valves which are at least partly designed as electrically controllable solenoid valves. A special electronic control unit serves to control these solenoid valves of the air suspension system. This separate electronic control unit is arranged at a different place than the electronic control unit of the compressed air processing apparatus. For example, it is arranged in the driver's cabin. In such a case, respective electric lines lead to the solenoid valves of the air suspension system. The structural and assembly expenditure required for these two electronic control units is substantial. The number of connections, electric lines and pneumatic conduits required in the motor vehicle is comparatively great.
A pneumatic air suspension system is known from European Patent Application No. EP 0 372 218 A2. The pneumatic air suspension system is arranged downstream of a source of compressed air including a compressed air processing apparatus. The pneumatic air suspension system is supplied with compressed air by a supply circuit branching off from the compressed air processing apparatus. Three valves are located in a control block, the valves being controlled by a separate electronic control unit. The valves are designed as directly controllable solenoid valves, but they may also be designed as electromagnetic pre-controlled valves which are pneumatically actuated. A first valve has two switching positions, and it is forced into a deaerating position by the force of a spring. The other position which is realized by electronic control is the position in which the deaerating opening is locked and in which there is connection such that there is compressed air at the exit of this valve, the compressed air coming from the circuit supplying the air suspension system with compressed air. The compressed air is fed to two valves which are also designed as directly actuatable electromagnetic valves. The valves are designed as locking valves, and they are associated with the left side and the right side of the motor vehicle and with the air suspension bellows being located at the left side and the right side, respectively. Path sensors are arranged close to the air suspension bellows. The signals of the path sensors are transmitted to the common control unit. Pressure sensors are arranged in the conduits leading to the air suspension bellows. The signals of the pressure sensors are also transmitted to the common electronic control unit. Such a known air suspension system requires the use of a separate electronic control unit and of respective connections to a compressed air processing apparatus. The structural expenditure and the assembly expenditure are substantial.